Antitumor activity of histone deacetylase inhibitors in non-small cell lung cancer cells: development of a molecular predictive model

Chromatin-targeting small molecules cause class-specific transcriptional changes in pancreatic endocrine cells

Under the instruction of cell-fate-determining, DNA-binding transcription factors, chromatin-modifying enzymes mediate and maintain cell states throughout development in multicellular organisms. Currently, small molecules modulating the activity of several classes of chromatin-modifying enzymes are available, including clinically approved histone deacetylase (HDAC) and DNA methyltransferase (DNMT) inhibitors. We describe the genome-wide expression changes induced by 29 compounds targeting HDACs, DNMTs, histone lysine methyltransferases (HKMTs), and protein arginine methyltransferases (PRMTs) in pancreatic α- and β-cell lines. HDAC inhibitors regulate several hundred transcripts irrespective of the cell type, with distinct clusters of dissimilar activity for hydroxamic acids and orthoamino anilides. In contrast, compounds targeting histone methyltransferases modulate the expression of restricted gene sets in distinct cell types. For example, we find that G9a/GLP methyltransferase inhibitors selectively up-regulate the cholesterol biosynthetic pathway in pancreatic but not liver cells. These data suggest that, despite their conservation across the entire genome and in different cell types, chromatin pathways can be targeted to modulate the expression of selected transcripts.

Enzastaurin has anti-tumour effects in lung cancers with overexpressed JAK pathway molecules

BACKGROUND

Enzastaurin, an oral serine-threonine kinase inhibitor, was initially developed as an ATP-competitive selective inhibitor against protein kinase Cβ. However, the mechanism by which enzastaurin contributes to tumourigenesis remains unclear.

METHODS

We analysed the anti-tumour effects of enzastaurin in 22 lung cancer cell lines to ascertain the potential for enzastaurin-based treatment of lung cancer. To identify molecules or signalling pathways associated with this sensitivity, we conducted a gene, receptor tyrosine kinases phosphorylation and microRNA expression profiling study on the same set of cell lines.

RESULTS

We identified eight genes by pathway analysis of molecules having gene-drug sensitivity correlation, and used them to build a support vector machine algorithm model by which sensitive cell lines were distinguished from resistant cell lines. Pathway analysis revealed that the JAK/STAT signalling pathway was one of the main ones involved in sensitivity to enzastaurin. Overexpression of JAK1 was observed in the sensitive cells by western blotting. Simultaneous administration of enzastaurin and JAK inhibitor inhibited enzastaurin-induced cell growth-inhibitory effect. Furthermore, lentiviral-mediated JAK1-overexpressing cells were more sensitive to enzastaurin than control cells.

CONCLUSION

Our results suggested that the JAK1 pathway may be used as a single predictive biomarker for enzastaurin treatment. The anti-tumour effect of enzastaurin should be evaluated in lung cancer with overexpressed JAK pathway molecules.

HDAC modulation and cell death in the clinic

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

Histone deacetylases (HDACs) as mediators of resistance to apoptosis in melanoma and as targets for combination therapy with selective BRAF inhibitors

HDACs are viewed as enzymes used by cancer cells to inhibit tumor suppressor mechanisms. In particular, we discuss their role as suppressors of apoptosis in melanoma cells and as mediators of resistance to selective BRAF inhibitors. Synergistic increases in apoptosis are seen when pan-HDAC inhibitors are combined with selective BRAF inhibitors. Moreover, cell lines from patients with acquired resistance to Vemurafenib undergo PLX4720 induced apoptosis when combined with pan-HDAC inhibitors. The mechanisms of upregulation of HDACs and the mechanisms involved in HDACi reversal of resistance to apoptosis are as yet poorly understood.

Vorinostat/SAHA-induced apoptosis in malignant mesothelioma is FLIP/caspase 8-dependent and HR23B-independent

INTRODUCTION

Malignant pleural mesothelioma (MPM) is a rapidly fatal malignancy that is increasing in incidence. The caspase 8 inhibitor FLIP is an anti-apoptotic protein over-expressed in several cancer types including MPM. The histone deacetylase (HDAC) inhibitor Vorinostat (SAHA) is currently being evaluated in relapsed mesothelioma. We examined the roles of FLIP and caspase 8 in regulating SAHA-induced apoptosis in MPM.

METHODS

The mechanism of SAHA-induced apoptosis was assessed in 7 MPM cell lines and in a multicellular spheroid model. SiRNA and overexpression approaches were used, and cell death was assessed by flow cytometry, Western blotting and clonogenic assays.

RESULTS

RNAi-mediated FLIP silencing resulted in caspase 8-dependent apoptosis in MPM cell line models. SAHA potently down-regulated FLIP protein expression in all 7 MPM cell lines and in a multicellular spheroid model of MPM. In 6/7 MPM cell lines, SAHA treatment resulted in significant levels of apoptosis induction. Moreover, this apoptosis was caspase 8-dependent in all six sensitive cell lines. SAHA-induced apoptosis was also inhibited by stable FLIP overexpression. In contrast, down-regulation of HR23B, a candidate predictive biomarker for HDAC inhibitors, significantly inhibited SAHA-induced apoptosis in only 1/6 SAHA-sensitive MPM cell lines. Analysis of MPM patient samples demonstrated significant inter-patient variations in FLIP and caspase 8 expressions. In addition, SAHA enhanced cisplatin-induced apoptosis in a FLIP-dependent manner.

CONCLUSIONS

These results indicate that FLIP is a major target for SAHA in MPM and identifies FLIP, caspase 8 and associated signalling molecules as candidate biomarkers for SAHA in this disease.

Differential response of cancer cells to HDAC inhibitors trichostatin A and depsipeptide

Background:

Over the last decade, several drugs that inhibit class I and/or class II histone deacetylases (HDACs) have been identified, including trichostatin A, the cyclic depsipeptide FR901228 and the antibiotic apicidin. These compounds have had immediate application in cancer research because of their ability to reactivate aberrantly silenced tumour suppressor genes and/or block tumour cell growth. Although a number of HDAC inhibitors are being evaluated in preclinical cancer models and in clinical trials, little is known about the differences in their specific mechanism of action and about the unique determinants of cancer cell sensitivity to each of these inhibitors.

Methods:

Using a combination of cell viability assays, HDAC enzyme activity measurements, western blots for histone modifications, microarray gene expression analysis and qRT–PCR, we have characterised differences in trichostatin A vs depsipeptide-induced phenotypes in lung cancer, breast cancer and skin cancer cells and in normal cells and have then expanded these studies to other HDAC inhibitors.

Results:

Cell viability profiles across panels of lung cancer, breast cancer and melanoma cell lines showed distinct sensitivities to the pan-inhibitor TSA compared with the class 1 selective inhibitor depsipeptide. In several instances, the cell lines most sensitive to one inhibitor were most resistant to the other inhibitor, demonstrating these drugs act on at least some non-overlapping cellular targets. These differences were not explained by the HDAC selectivity of these inhibitors alone since apicidin, which is a class 1 selective compound similar to depsipeptide, also showed a unique drug sensitivity profile of its own. TSA had greater specificity for cancer vs normal cells compared with other HDAC inhibitors. In addition, at concentrations that blocked cancer cell viability, TSA effectively inhibited purified recombinant HDACs 1, 2 and 5 and moderately inhibited HDAC8, while depsipeptide did not inhibit the activity of purified HDACs in vitro but did in cellular extracts, suggesting a potentially indirect action of this drug. Although both depsipeptide and TSA increased levels of histone acetylation in cancer cells, only depsipeptide decreased global levels of transcriptionally repressive histone methylation marks. Analysis of gene expression profiles of an isogenic cell line pair that showed discrepant sensitivity to depsipeptide, suggested that resistance to this inhibitor may be mediated by increased expression of multidrug resistance genes triggered by exposure to chemotherapy as was confirmed by verapamil studies.

Conclusion:

Although generally thought to have similar activities, the HDAC modulators trichostatin A and depsipeptide demonstrated distinct phenotypes in the inhibition of cancer cell viability and of HDAC activity, in their selectivity for cancer vs normal cells, and in their effects on histone modifications. These differences in mode of action may bear on the future therapeutic and research application of these inhibitors.

HDAC inhibitors in cancer biology: emerging mechanisms and clinical applications

Reversible acetylation mediated by histone deacetylases (HDACs) influences a broad repertoire of physiological processes, many of which are aberrantly controlled in tumor cells. As HDAC inhibition prompts tumor cells to enter apoptosis, small-molecule HDAC inhibitors have been developed as a new class of mechanism-based anti-cancer agent, many of which have entered clinical trials. Although the clinical picture is evolving and the precise utility of HDAC inhibitors remains to be determined, it is noteworthy that certain tumor types undergo a favorable response, in particular hematological malignancies. Vorinostat and romidepsin have been approved for treating cutaneous T-cell lymphoma in patients with progressive, persistent or recurrent disease. Here, we discuss developments in our understanding of molecular events that underlie the anti-cancer effects of HDAC inhibitors and relate this information to the emerging clinical picture for the application of these inhibitors in the treatment of cancer.

SAHA Capture Compound--a novel tool for the profiling of histone deacetylases and the identification of additional vorinostat binders

Suberoylanilide hydroxamic acid (SAHA) is a potent histone deacetylase (HDAC) inhibitor. Inhibitors of HDACs are used in cancer therapy based on the role HDACs play in transcription by regulating chromatin compaction and non-histone proteins such as transcription factors. Profiling of HDAC expression is of interest in the functional proteomics analysis of cancer. Also, non-HDAC proteins may interact with HDAC inhibitor drugs and contribute to the drug mode of action. We here present a tool for the unbiased chemical proteomic profiling of proteins that specifically interact with SAHA. We designed and synthesized a trifunctional Capture Compound containing SAHA as selectivity and identified HDACs1, 2, 3 and 6, known and predicted HDAC interactors from human-derived HepG2 cell lysate, as well as a set of new potential non-HDAC targets of SAHA. One of these non-HDAC targets, isochorismatase domain-containing protein 2 (ISOC2) is putative hydrolase associated with the negative regulation of the tumor-suppressor p16(INK4a). We demonstrated the direct and dose-dependent interaction of SAHA to the purified recombinant ISOC2 protein. Using SAHA Capture Compound mass spectrometry, we thus identified potential new SAHA target proteins in an entirely unbiased chemical proteomics approach.

Metabolism as a key to histone deacetylase inhibition

There is growing interest in the epigenetic mechanisms that are dysregulated in cancer and other human pathologies. Under this broad umbrella, modulators of histone deacetylase (HDAC) activity have gained interest as both cancer chemopreventive and therapeutic agents. Of the first generation, FDA-approved HDAC inhibitors to have progressed to clinical trials, vorinostat represents a "direct acting" compound with structural features suitable for docking into the HDAC pocket, whereas romidepsin can be considered a prodrug that undergoes reductive metabolism to generate the active intermediate (a zinc-binding thiol). It is now evident that other agents, including those in the human diet, can be converted by metabolism to intermediates that affect HDAC activity. Examples are cited of short-chain fatty acids, seleno-α-keto acids, small molecule thiols, mercapturic acid metabolites, indoles, and polyphenols. The findings are discussed in the context of putative endogenous HDAC inhibitors generated by intermediary metabolism (e.g. pyruvate), the yin-yang of HDAC inhibition versus HDAC activation, and the screening assays that might be most appropriate for discovery of novel HDAC inhibitors in the future.

Expression of histone deacetylase 1 correlates with a poor prognosis in patients with adenocarcinoma of the lung

Histone deacetylase (HDAC) inhibitors (HDACis) are now attracting attention as promising therapeutic agents for the treatment of cancer. However, the relation between HDAC1 expression and the clinicopathological characteristics of non-small cell lung cancer (NSCLC) is not well understood. We therefore investigated the relationship between HDAC1 expression by tumors and the clinicopathological characteristics of patients with adenocarcinoma of the lung.

METHODS

We used semi-quantitative real time reverse transcription polymerase chain reaction to assess expression of HDAC1 mRNA in tumor samples from 93 patients with adenocarcinoma of the lung. We then correlated HDAC1 mRNA levels with known clinicopathological factors.

RESULTS

We found that the 5-year disease-free survival rate among patients strongly expressing HDAC1 was significantly poorer than among those expressing lower levels (P=0.005 by log-rank test). Multivariate Cox proportional hazard analyses revealed that being male (hazard ratio, 3.56; 95% CI, 1.58-8.42; P=0.002), nodal metastasis (hazard ratio, 7.98; 95% CI, 2.99-22.1; P<.001) and HDAC1 (hazard ratio, 2.17; 95% CI, 1.04-4.84; P=0.039) were all independent factors affecting 5-year disease-free survival.

CONCLUSION

Stronger HDAC1 expression by tumor cells is an independent predictor of a poor prognosis in patients with adenocarcinoma of the lung.

[Histone deacetylase inhibitors: highlight on epigenetic regulation]

HDAC, by modifiing relations between DNA and histones, are major proteins of the epigenetic regulation. They play part in the signal transduction and in many cellular processes: cell cycle control, apoptosis, protein degradation, angiogenesis, invasion and cell motility. In several models of cancer HDAC inhibitors (HDACIs) are able to up regulate tumor suppressing gene (p53, p21, pRB...) and to down regulate oncogenes (SRC, HIF-Ialpha,HER2...). Many inhibitors are currently in clinical development and promising results have been reported in cutaneous T cell lymphoma, Hodgkin's disease and non-hodgkin lymphoma. Combination with chemotherapy and molecular targeted agents seem to be effective in myeloma, lung cancer and myeloïd neoplasms. In this review, we focus on recent biologic and clinical data that highlitght the anti-neoplastic role of HDACIs.

Comparative analysis of nonaspanin protein sequences and expression studies in zebrafish

Nonaspanins constitute a family of proteins, also called TM9SF, characterized by a large non-cytoplasmic domain and nine putative transmembrane domains. This family is highly conserved through evolution and comprises three members in Saccharomyces cerevisiae, Dictyostelium discoideum, and Drosophila melanogaster, and four members are reported in mammals (TM9SF1-TM9SF4). Genetic studies in Dictyostelium and Drosophila have shown that TM9SF members are required for adhesion and phagocytosis in innate immune response, furthermore, human TM9SF1 plays a role in the regulation of autophagy and human TM9SF4 in tumor cannibalism. Here we report that the zebrafish genome encodes five members of this family, TM9SF1-TM9SF5, which show high level of sequence conservation with the previously reported members. Expression analysis in zebrafish showed that all members are maternally expressed and continue to be present throughout embryogenesis to adults. Gene expression could not be regulated by pathogen-associated molecular patterns such as LPS, CpG, or Poly I:C. By bioinformatic analyses of 80 TM9SF protein sequences from yeast, plants, and animals, we confirmed a very conserved protein structure. An evolutionary conserved immunoreceptor tyrosine-based inhibition motif has been detected in the cytoplasmic domain between transmembrane domain (TM) 7 and TM8 in TM9SF1, TM9SF2, TM9SF4 and TM9SF5, and at the extreme C-terminal end of TM9SF4. Finally, a conserved TRAF2 binding domain could also be predicted in the cytoplasmic regions of TM9SF2, TM9SF3, TM9SF4, and TM9SF5. This confirms the hypothesis that TM9SF proteins may play a regulatory role in a specific and ancient cellular mechanism that is involved in innate immunity.

Histone deacetylase inhibitor enhances sensitivity of non-small-cell lung cancer cells to 5-FU/S-1 via down-regulation of thymidylate synthase expression and up-regulation of p21(waf1/cip1) expression

It is desirable to find more appropriate therapeutic opportunities in non-small-cell lung cancer (NSCLC) due to the current poor prognosis of affected patients. Recently, several histone deacetylase (HDAC) inhibitors, including suberoylanilide hydroxamic acid (SAHA), have been reported to exhibit antitumor activities against NSCLC. S-1, a novel oral fluorouracil anticancer drug, has been developed for clinical use in the treatment of NSCLC in Japan. Using an MTT assay, we analyzed the growth-inhibitory effect of 5-fluorouracil (5-FU), S-1, and SAHA against three NSCLC cell lines, as well as the breast cancer cell line MCF7 which is known to be highly sensitive to 5-FU. Combined treatment with low-dose SAHA enhanced 5-FU- and S-1-mediated cytotoxicity and resulted in synergistic effects, especially in 5-FU-resistant cells. Both the mRNA and protein expression levels of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and orotate phosphoribosyltransferase (OPRT), which are associated with 5-FU sensitivity/response, were analyzed in the cells undergoing treatment. 5-Fluorouracil-resistant lung cancer cells displayed high expression of TS mRNA and protein. Suberoylanilide hydroxamic acid down-regulated TS mRNA and protein expression, as well as repressed the rapid induction of this factor during 5-FU treatment, in all examined cell types. We also examined the status of the Rb-E2F1 pathway, with SAHA up-regulating p21(waf1/cip1) expression via promoter histone acetylation; this, in turn, blocked the Rb-E2F1 pathway. We conclude that combination therapy with SAHA and S-1 in lung cancer may be promising due to its potential to overcome S-1 resistance via modulation of 5-FU/S-1 sensitivity-associated biomarker (TS) by HDAC inhibitor.

Identification of genes related to a synergistic effect of taxane and suberoylanilide hydroxamic acid combination treatment in gastric cancer cells

PURPOSE

We evaluated the cytotoxic effects of combining suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, with taxanes in human gastric cancer cell lines and assessed the pre-treatment difference of gene expression to identify genes that could potentially mediate the cytotoxic response.

METHODS

Gastric cancer cell lines were treated with SAHA and paclitaxel or docetaxel, and the synergistic interaction between the drugs was evaluated in vitro using the combination index (CI) method. We performed significance analysis of microarray (SAM) to identify chemosensitivity-related genes in gastric cancer cell lines that were concomitantly treated with SAHA and taxane. We generated a correlation matrix between gene expression and CI values to identify genes whose expression correlated with a combined effect of taxanes and SAHA.

RESULTS

Combination treatment with taxane and SAHA had a synergistic cytotoxic effect against taxane-resistant gastric cancer cells. We identified 49 chemosensitivity-related genes via SAM analysis. Among them, nine common genes (SLIT2, REEP2, EFEMP2, CDC42SE1, FSD1, POU1F1, ZNF79, ETNK1, and DOCK5) were extracted from the subsequent correlation matrix analysis.

CONCLUSIONS

The combination of taxane and SAHA could be efficacious for the treatment of gastric cancer. The genes that were related to the synergistic response to taxane and SAHA could serve as surrogate biomarkers to predict the therapeutic response in gastric cancer patients.

Induction of E-cadherin in lung cancer and interaction with growth suppression by histone deacetylase inhibition

INTRODUCTION

Loss of E-cadherin confers a poor prognosis in lung cancer patients and is associated with in vitro resistance to endothelial growth factor receptor inhibitors. Zinc finger E box-binding homeobox (ZEB)-1, the predominant transcriptional suppressor of E-cadherin in lung tumor lines, recruits histone deacetylases (HDACs) as co-repressors.

METHODS

NSCLC cell lines were treated with HDAC inhibitors and analyzed for E-cadherin induction, growth inhibition and apoptosis. National Cancer Institute-H157 cells expressing ectopic E-cadherin were tested for tumorigenicity in murine xenografts.

RESULTS

We found that treatment with MS-275, compared to vorinostat (SAHA), valproic acid or trichostatin A, was most effective in E-cadherin up-regulation and persistence in non-small cell lung cancers. As with other tumor types and HDAC inhibitors, MS-275 inhibited growth and induced apoptosis. Importantly, blocking E-cadherin induction by short hairpin RNA resulted in less inhibition by MS-275, implicating the epithelial to mesenchymal phenotype process as a contributing factor. In contrast to H460 and H661, H157 cells were resistant to E-cadherin up-regulation by HDAC inhibitors. However, E-cadherin was restored, in a synergistic manner, by combined knockdown of ZEB-1 and ZEB-2. In addition, H157 cells stably transfected with E-cadherin were markedly attenuated in their tumor forming ability. Lastly, combining MS-275 with the microtubule stabilizing agent, paclitaxel, or 17-(allylamino)-17-demethoxygeldanamycin, a heat shock protein 90 inhibitor, resulted in synergistic growth inhibition. Since MS-275 has no reported activity against HDAC6, which regulates both microtubule and heat shock protein 90 functions, other mechanisms of synergy are anticipated.

CONCLUSIONS

These results support the role of ZEB proteins and HDAC inhibitors in the pathogenesis and treatment of lung cancer.

Histone deacetylase inhibitors in cancer therapy

PURPOSE

Epigenetic processes are implicated in cancer causation and progression. The acetylation status of histones regulates access of transcription factors to DNA and influences levels of gene expression. Histone deacetylase (HDAC) activity diminishes acetylation of histones, causing compaction of the DNA/histone complex. This compaction blocks gene transcription and inhibits differentiation, providing a rationale for developing HDAC inhibitors.

METHODS

In this review, we explore the biology of the HDAC enzymes, summarize the pharmacologic properties of HDAC inhibitors, and examine results of selected clinical trials. We consider the potential of these inhibitors in combination therapy with targeted drugs and with cytotoxic chemotherapy.

RESULTS

HDAC inhibitors promote growth arrest, differentiation, and apoptosis of tumor cells, with minimal effects on normal tissue. In addition to decompaction of the histone/DNA complex, HDAC inhibition also affects acetylation status and function of nonhistone proteins. HDAC inhibitors have demonstrated antitumor activity in clinical trials, and one drug of this class, vorinostat, is US Food and Drug Administration approved for the treatment of cutaneous T-cell lymphoma. Other inhibitors in advanced stages of clinical development, including depsipeptide and MGCD0103, differ from vorinostat in structure and isoenzyme specificity, and have shown activity against lymphoma, leukemia, and solid tumors. Promising preclinical activity in combination with cytotoxics, inhibitors of heat shock protein 90, and inhibitors of proteasome function have led to combination therapy trials.

CONCLUSION

HDAC inhibitors are an important emerging therapy with single-agent activity against multiple cancers, and have significant potential in combination use.

The HDAC inhibitor panobinostat (LBH589) inhibits mesothelioma and lung cancer cells in vitro and in vivo with particular efficacy for small cell lung cancer

Lung cancer is the leading cause of cancer deaths in the United States. Current therapies are inadequate. Histone deacetylase inhibitors (HDACi) are a recently developed class of anticancer agents that cause increased acetylation of core histones and nonhistone proteins leading to modulation of gene expression and protein activity involved in cancer cell growth and survival pathways. We examined the efficacy of the HDACi panobinostat (LBH589) in a wide range of lung cancers and mesotheliomas. Panobinostat was cytotoxic in almost all 37 cancer cell lines tested. IC(50) and LD(50) values were in the low nmol/L range (4-470 nmol/L; median, 20 nmol/L). Small cell lung cancer (SCLC) cell lines were among the most sensitive lines, with LD(50) values consistently <25 nmol/L. In lung cancer and mesothelioma animal models, panobinostat significantly decreased tumor growth by an average of 62% when compared with vehicle control. Panobinostat was equally effective in immunocompetent and severe combined immunodeficiency mice, indicating that the inhibition of tumor growth by panobinostat was not due to direct immunologic effects. Panobinostat was, however, particularly effective in SCLC xenografts, and the addition of the chemotherapy agent etoposide augmented antitumor effects. Protein analysis of treated tumor biopsies revealed elevated amounts of cell cycle regulators such as p21 and proapoptosis factors, such as caspase 3 and 7 and cleaved poly[ADP-ribose] polymerase, coupled with decreased levels of antiapoptotic factors such as Bcl-2 and Bcl-X(L). These studies together suggest that panobinostat may be a useful adjunct in the treatment of thoracic malignancies, especially SCLC.

Alpha-keto acid metabolites of organoselenium compounds inhibit histone deacetylase activity in human colon cancer cells

Methylselenocysteine (MSC) and selenomethionine (SM) are two organoselenium compounds receiving interest for their potential anticancer properties. These compounds can be converted to beta-methylselenopyruvate (MSP) and alpha-keto-gamma-methylselenobutyrate (KMSB), alpha-keto acid metabolites that share structural features with the histone deacetylase (HDAC) inhibitor butyrate. We tested the organoselenium compounds in an in vitro assay with human HDAC1 and HDAC8; whereas SM and MSC had little or no activity up to 2 mM, MSP and KMSB caused dose-dependent inhibition of HDAC activity. Subsequent experiments identified MSP as a competitive inhibitor of HDAC8, and computational modeling supported a mechanism involving reversible interaction with the active site zinc atom. In human colon cancer cells, acetylated histone H3 levels were increased during the period 0.5-48 h after treatment with MSP and KMSB, and there was dose-dependent inhibition of HDAC activity. The proportion of cells occupying G(2)/M of the cell cycle was increased at 10-50 microM MSP and KMSB, and apoptosis was induced, as evidenced by morphological changes, Annexin V staining and increased cleaved caspase-3, -6, -7, -9 and poly(adenosine diphosphate-ribose)polymerase. P21WAF1, a well-established target gene of clinically used HDAC inhibitors, was increased in MSP- and KMSB-treated colon cancer cells at both the messenger RNA and protein level, and there was enhanced P21WAF1 promoter activity. These studies confirm that in addition to targeting redox-sensitive signaling molecules, alpha-keto acid metabolites of organoselenium compounds alter HDAC activity and histone acetylation status in colon cancer cells, as recently observed in human prostate cancer cells.

Cytotoxicity mediated by histone deacetylase inhibitors in cancer cells: mechanisms and potential clinical implications

Aberrant expression of epigenetic regulators of gene expression contributes to initiation and progression of cancer. During recent years, considerable research efforts have focused on the role of histone acetyltransferases (HATs) and histone deacetylases (HDACs) in cancer cells, and the identification of pharmacologic agents that modulate gene expression via inhibition of HDACs. The following review highlights recent studies pertaining to HDAC expression in cancer cells, the plieotropic mechanisms by which HDAC inhibitors (HDACi) mediate antitumor activity, and the potential clinical implications of HDAC inhibition as a strategy for cancer therapy.

Biomarkers for predicting clinical responses to HDAC inhibitors

Post-translational modifications of histone and non-histone proteins by acetylation are known to play a key role in tumourigenesis. Pharmacological manipulation of acetylation has been possible with the identification of small molecule inhibitors of histone deacetylases (HDAC), the enzymes responsible for deacetylating lysine residues. An explosion of drug discovery efforts in recent years has led to the development of an extensive group of HDAC inhibitors, many of which have been shown pre-clinically to have potent anti-tumour activity. Clinical trials using these agents are now underway, with Vorinostat (suberoylanilide hydroxamic acid) having been approved by the FDA for treating cutaneous T-cell lymphoma (CTCL) in patients with progressive, persistent or recurrent disease. This review discusses how biomarkers are being identified and used to expand our knowledge of the mechanisms by which HDAC inhibitors exhibit their anti-cancer effects. In the longer term, biomarkers will provide a means towards achieving patient stratification in tumour types that will respond favourably to HDAC inhibitors.

Lung cancer and chronic obstructive pulmonary disease: needs and opportunities for integrated research

Lung cancer and chronic obstructive pulmonary disease (COPD) are leading causes of morbidity and mortality in the United States and worldwide. They share a common environmental risk factor in cigarette smoke exposure and a genetic predisposition represented by the incidence of these diseases in only a fraction of smokers. The presence of COPD increases the risk of lung cancer up to 4.5-fold. To investigate commonalities in disease mechanisms and perspectives for disease chemoprevention, the National Heart, Lung, and Blood Institute (NHLBI) and the National Cancer Institute (NCI) held a workshop. The participants identified four research objectives: 1) clarify common epidemiological characteristics of lung cancer and COPD; 2) identify shared genetic and epigenetic risk factors; 3) identify and validate biomarkers, molecular signatures, and imaging-derived measurements of each disease; and 4) determine common and disparate pathogenetic mechanisms. These objectives should be reached via four research approaches: 1) identify, publicize, and enable the evaluation and analysis of existing datasets and repositories of biospecimens; 2) obtain phenotypic and outcome data and biospecimens from large studies of subjects with and/or at risk for COPD and lung cancer; 3) develop and use animal and other preclinical models to investigate pathogenetic links between the diseases; and 4) conduct early-phase clinical trials of potential chemopreventive agents. To foster much needed research interactions, two final recommendations were made by the participants: 1) incorporate baseline phenotyping and outcome measures for both diseases in future longitudinal studies of each disease and 2) expand collaborative efforts between the NCI and NHLBI.

Vorinostat (NSC# 701852) in patients with relapsed non-small cell lung cancer: a Wisconsin Oncology Network phase II study

INTRODUCTION

Vorinostat is a small molecule inhibitor of histone deacetylase, and has shown preclinical activity in non-small cell lung cancer (NSCLC).

METHODS

Patients with relapsed NSCLC were eligible. Patients received oral vorinostat, 400 mg daily. The primary objective was response rate, with the goal of at least one responder in the first 14 evaluable patients, according to the two-stage minimax design. Secondary objectives included time to progression (TTP), overall survival (OS), and safety.

RESULTS

Sixteen patients enrolled from January 2006 to April 2007. The median age was 59.5 years. Thirteen patients were female. Two patients were not evaluable for response due to progressive disease within Cycle 1. No objective antitumor responses were seen in the 14 evaluable patients. Eight patients experienced stable disease (median 3.7 months, range 1.4-19.4). Median TTP was 2.3 months (range 0.9-19.4 months), median OS was 7.1 months (range 1.4-30.0+ months), and estimated 1 year OS rate was 19% (SE 10%). One patient died on study from an acute ischemic stroke; this event was deemed possibly related to treatment. Grade 3/4 adverse events possibly related to vorinostat included neutropenia, lymphopenia, fatigue, pulmonary embolus/deep vein thrombosis, dehydration, elevated alkaline phosphatase, and hypokalemia.

CONCLUSIONS

No objective antitumor activity was detected with single agent vorinostat in this setting; however, it yields TTP in relapsed NSCLC similar to that of other targeted agents. Further studies in NSCLC should focus on combining vorinostat with other antitumor agents.

Targeting histone deacetylases for the treatment of disease

The ‘histone code’ is a well-established hypothesis describing the idea that specific patterns of post-translational modifications to histones act like a molecular ‘code’ recognized and used by non-histone proteins to regulate specific chromatin functions. One modification, which has received significant attention, is that of histone acetylation. The enzymes that regulate this modification are described as lysine acetyltransferases or KATs, and histone deacetylases or HDACs. Due to their conserved catalytic domain HDACs have been actively targeted as a therapeutic target. The pro-inflammatory environment is increasingly being recognized as a critical element for both degenerative diseases and cancer. The present review will discuss the current knowledge surrounding the clinical potential and current development of histone deacetylases for the treatment of diseases for which a pro-inflammatory environment plays important roles, and the molecular mechanisms by which such inhibitors may play important functions in modulating the pro-inflammatory environment.